Bridging the computational gap between mesoscopic and continuum modeling of red blood cells for fully resolved blood flow

We present a computational framework for the simulation of blood flow with fully resolved red blood cells (RBCs) using a modular approach that consists of a lattice Boltzmann solver for the blood plasma, a novel finite element based solver for the deformable bodies and an immersed boundary method for the fluid-solid interaction. For the RBCs, we propose a nodal projective FEM (npFEM) solver which has theoretical advantages over the more commonly used mass-spring systems (mesoscopic modeling), such as an unconditional stability, versatile material expressivity, and one set of parameters to fully describe the behavior of the body at any mesh resolution. At the same time, the method is substantially faster than other FEM solvers proposed in this field, and has an efficiency that is comparable to the one of mesoscopic models. At its core, the solver uses specially defined potential energies, and builds upon them a fast iterative procedure based on quasi-Newton techniques. For a known material, our solver has only one free parameter that demands tuning, related to the body viscoelasticity. In contrast, state-of-the-art solvers for deformable bodies have more free parameters, and the calibration of the models demands special assumptions regarding the mesh topology, which restrict their generality and mesh independence. We propose as well a modification to the potential energy proposed by Skalak et al. 1973 for the red blood cell membrane, which enhances the strain hardening behavior at higher deformations. Our viscoelastic model for the red blood cell, while simple enough and applicable to any kind of solver as a post-convergence step, can capture accurately the characteristic recovery time and tank-treading frequencies. The framework is validated using experimental data, and it proves to be scalable for multiple deformable bodies

Spatial Coupling of a Lattice Boltzmann fluid model with a Finite Difference Navier-Stokes solver

In multiscale, multi-physics applications, there is an increasing need for coupling numerical solvers that are each applied to a different part of the problem. Here we consider the case of coupling a Lattice Boltzmann fluid model and a Finite Difference Navier-Stokes solver. The coupling is implemented so that the entire computational domain can be divided in two regions, with the FD solver running on one of them and the LB one on the other. We show how the various physical quantities of the two approaches should be related to ensure a smooth transition at the interface between the regions. We demonstrate the feasibility of the method on the Poiseuille flow, where the LB and FD schemes are used on adjacent sub-domains. The same idea can be also developed to couple LB models with Finite Volumes, or Finite Elements calculations. The motivation for developing such a type of coupling is that, depending on the geometry of the flow, one technique can be more efficient, less memory consuming, or physically more appropriate than the other in some regions (e.g. near the boundaries), whereas the converse is true for other parts of the same system. We can also imagine that a given system solved, say by FD, can be augmented in some spatial regions with a new physical process that is better treated by a LB model. Our approach allows us to only modify the concerned region without altering the rest of the computation.Comment: 10 pages, 2 figure

Trial and settlement negotiations between asymmetrically skilled parties

Parties engaged in a litigation generally enter the discovery process with different informations regarding their case and/or an unequal endowment in terms of skill and ability to produce evidence and predict the outcome of a trial. Hence, they have to bear different legal costs to assess the (equilibrium) plaintiff's win rate. The paper analyses pretrial negotiations and revisits the selection hypothesis in the case where these legal expenditures are private information. This assumption is consistent with empirical evidence (Osborne, 1999). Two alternative situations are investigated, depending on whether there exists a unilateral or a bilateral informational asymmetry.\ Our general result is that efficient pretrial negotiations select cases with the smallest legal expenditures as those going to trial, while cases with largest costs prefer to settle. Under the one-sided asymmetric information assumption, we find that the American rule yields more trials and higher aggregate legal expenditures than the French and British rules. The two-sided case leads to a higher rate of trials, but in contrast provides less clear-cut predictions regarding the influence of fee-shifting.litigation, unilateral and bilateral asymmetric information, legal expenditures

Competing Species Dynamics: Qualitative Advantage versus Geography

A simple cellular automata model for a two-group war over the same territory is presented. It is shown that a qualitative advantage is not enough for a minority to win. A spatial organization as well a definite degree of aggressiveness are instrumental to overcome a less fitted majority. The model applies to a large spectrum of competing groups: smoker-non smoker war, epidemic spreading, opinion formation, competition for industrial standards and species evolution. In the last case, it provides a new explanation for punctuated equilibria.Comment: 7 pages, latex, 2 figures include

Marketing A Hospitality Program And Its Product

In his dialogue entitled - Marketing A Hospitality Program and Its Product - Jürgen Chopard, Dr. es Sciences (Economics) Director, Centre International de Glion, Glion, Switzerland, Dr. Chopard initially offers: “The recruitment of qualified personnel is extremely difficult in an industry with a poor image; where career paths are not well defined. The author discusses the employment of marketing management techniques to improve the positioning of hospitality education and create a more attractive perception of the hotel industry.” As outlined in the above paragraph, Dr. Chopard vectors-in on marketing strategies from two standpoints; the educational side with its focus on curriculum, and the larger, industry side with its emphasis on public perception and service. These are not necessarily, nor should they be viewed as disparate elements. “ Although some professionals may see schools of hospitality education catering to two markets, students on one hand and industry on the other, in fact, their needs should be viewed as the same and hence a single market,” Dr. Chopard says to bolster his assertion. “The marketing concept is a management orientation that holds that the key task of the organization is to determine the needs and wants of target markets and to adapt the organization to delivering the desired satisfactions more effectively and efficiently than its competitor,” the author confides, with an attribution. From these information/definition leanings, Dr. Chopard continues on a path that promotes the Centre International de Glion, Glion, Switzerland, which he is affiliated with. Why, because they endorse the same principles he is explaining to you. That’s not a bad thing. Essentially, what Dr. Chopard wants you to know is, education and business management are synonymous and therefore should share the same marketing designs and goals. “It is hard to believe that as critically important a sector as education does not use for its own management the techniques which it teaches and which have largely been proved in other fields,” the author provides as counterpoint. Since pedagogical needs so closely relate to the more pragmatic needs of the industry in general, these elements should seek to compliment and engage each other, in fact, collaboration is imperative, Dr. Chopard expresses a priori. “The cooperation of future employers is indispensable in the preparation of the product, so that it is capable of providing the expected services. The need for close relations between training establishments and the hotel and catering industry seems obvious,” Dr. Chopard says. The author reveals some flaws in hospitality marketing strategy, and then contrasts these against how a successful strategy could/should be implemented

Voyage de Ch. Alluaud et R. Jeannel en Afrique Orientale (1911-1912) (Gryllidae)

Ainsi que je l'ai déjà indiqué pour les Mantides , l'Afrique Orientale ne peut en aucune façon être considérée comme une région zoogéographique délimitée. Le Catalogue que je donne ci-dessous n'a donc d'autre but que de faire connaître les espèces récoltées dans la région, et par là même, de faciliter les recherches et les déterminations futures.Peer reviewe

Les divisions du genre Gryllus basees sur l'étude de l'appareil copulateur (Orth. Gryllidae)

13 láminasDans un travail récent (1954), j'ai fait ressortir les difficultés que les systématiciens recontrent pour séparer les nombreuses espèces du genre Gryllus. J'ai indiqué que, parmi les caractères utilisés dans ce but, l'appareil copulateur du /riffle semble étre le plus valabie et le plus constant. Toutefois, j'indiquais en méme temps qu'il ne semblait pas qu'on puisse demander davantage à ce caractére et en particulier, qu'il ne permettait pas d'établir des divisions d'ordre générique. Je dois revenir aujourd'hui sur cette question. L'étude que j'ai poursuivie de l'organe copulateur des Gryllus m'a permis d'examiner plus de la moitié des quelque deux cents espéces actuellement classées dans ce genre. La comparaison des nombreuses formes étudiées amène en effet à les grouper en plusieurs catégories assez nettement caractérisées. Ce groupement permet de confirmer les affinttés qui avaient été mises en valeur par des méthodes différentes. Le cas le plus typique est celui qui permet de rapprocher par un caractère anatomique les espéces américaines du genre Gryllus et deux de nos espèces françaises (Gryllus campestris et G. bimaculatus) dont les affinités étroites avaient déja été mises en évidence par les résultats des croisements interspécifiques réalisés par Mlle. Cousin.Peer reviewe